Repair of a Bacterial Small β-Barrel Toxin Pore Depends on Channel Width

Membrane repair emerges as an innate defense protecting target cells against bacterial pore-forming toxins. Here, we report the first paradigm of Ca(2+)-dependent repair following attack by a small β-pore-forming toxin, namely, plasmid-encoded phobalysin of Photobacterium damselae subsp. damselae. In striking contrast, Vibrio cholerae cytolysin, the closest ortholog of phobalysin, subverted repair. Mutational analysis uncovered a role of channel width in toxicity and repair. Thus, the replacement of serine at phobalysin´s presumed channel narrow point with the bulkier tryptophan, the corresponding residue in Vibrio cholerae cytolysin (W318), modulated Ca(2+) influx, lysosomal exocytosis, and membrane repair. And yet, replacing tryptophan (W318) with serine in Vibrio cholerae cytolysin enhanced toxicity. The data reveal divergent strategies evolved by two related small β-pore-forming toxins to manipulate target cells: phobalysin leads to fulminant perturbation of ion concentrations, closely followed by Ca(2+) influx-dependent membrane repair. In contrast, V. cholerae cytolysin causes insidious perturbations and escapes control by the cellular wounded membrane repair-like response.